This invention relates to semiconductor devices comprising both a bipolar transistor and an insulated-gate field-effect transistor, particularly but not exclusively for rapid power switching applications.
The paper entitled "Design Considerations for FET-Gated Power Transistors" by D. Y. Chen and S. A. Chin, pages 144 to 149 of the 1983 IEEE Proceedings of the Power Electronic Specialist Conference, IEEE publication 0275-9306/83/0000-0144, describes a semiconductor device comprising a bipolar transistor of vertical configuration having an emitter region of one conductivity type in a base region of the opposite conductivity type. The base region is provided in a higher resistivity body portion of the one conductivity type which forms at least part of a collector region of the bipolar transistor. The device additionally comprises an insulated-gate field-effect transistor (designated as FET) connected to the base region.
A hybrid connection in a common device package of at least three semiconductor bodies (called "chips") is proposed in the Chen and Chin paper to form a so-called "FET-bipolar combination transistor configuration" having three terminals. The transistor configuration consists of the bipolar transistor Q.sub.1, two FETs Q.sub.2 and Q.sub.3 and a zener diode Z. The FETs Q.sub.2 and Q.sub.3 have insulated gates connected together and individual source and drain regions which are of the same conductivity type as the emitter and collector regions of the bipolar transistor.
The FET Q.sub.2 may be formed in the same semiconductor body as the bipolar transistor (as illustrated in FIG. 3 of the Chen and Chin paper) and provides current to the base region of the bipolar transistor to turn on the transistor configuration. The FET Q.sub.3 which is formed in a separate semiconductor body from that of the bipolar transistor Q.sub.1 provides a gateable connection to the emitter region of the bipolar transistor to open-circuit the emitter when turning off the bipolar transistor Q.sub.1. The zener diode also formed in a separate semiconductor body provides a charge-extraction path from the base region of the bipolar transistor when turning off the bipolar transistor Q.sub.1.
This hybrid connection of at least three semiconductor device bodies results in an expensive device arrangement. Although FET Q.sub.2 may be formed in the same body as the bipolar transistor, it is not easy to form the zener diode in the same body (at least not in a compact structure). Furthermore, a disadvantage of using a zener diode for the base charge extraction is that significant transient dissipation occurs at the zener voltage during turn off.